A thrust bearing is a component in a gas turbine engine that is designed to support other components of the gas turbine engine and to brace such other components against the thrust that they generate. One engine sub-assembly that is supported by a thrust bearing is commonly referred to as the spool. The spool includes a shaft, a compressor that may include an impeller or axial stages, and a turbine. The compressor and the turbine are mounted to the shaft and rotate together with the shaft. The compressor and the turbine each generate thrust that acts on the spool. The compressor generates thrust on the spool that pushes the spool towards the front of the engine while the turbine generates thrust that pushes the spool towards the rear of the engine. These oppositely directed thrusts are rarely, if ever equal. Consequently a net or resultant thrust acting in either the forward or rearward direction will be exerted on the spool as a result of the differing magnitudes of these oppositely directed forces (hereinafter, the “spool thrust”). The thrust bearing supports and braces the spool against the spool thrust to inhibit the spool from being displaced from its mounted position within the gas turbine engine.
Computational models are available that enable engine designers to estimate the direction and magnitude of the spool thrust that will be generated by a spool when designing and developing new gas turbine engines. These estimates are then used to design thrust bearings that will be sufficiently robust to support and brace the spool against the anticipated spool thrust. However, the computational models are not exact and it is often the case that the direction and/or the magnitude of the spool thrust of the spool, once built, differs from what was predicted by such models.
If the difference between the anticipated spool thrust and the actual spool thrust differs substantially, then the thrust bearing will be required to brace the spool against significantly more or significantly less spool thrust than it was designed to accommodate. If too much spool thrust is exerted on the thrust bearing, in either the forward or rearward direction, the ball bearings in the thrust bearing can damage their housing. If excessive spool thrust is continued for any length of time, the thrust bearing may fail. If too little spool thrust is exerted on the thrust bearing, then there will be an insufficient amount of friction acting on the ball bearings in the thrust bearing, causing them to skip and skid. This, in turn, may also damage their housing and may also lead to failure of the thrust bearing.
When the actual spool thrust differs substantially from the anticipated spool thrust, the conventional solution has been to redesign the thrust bearings to accommodate the actual spool thrust. Although this solution is adequate, the amount of time needed to design, develop and manufacture new thrust bearings is quite substantial. Thus, this solution can delay engine development by months or years which, in turn, can cost the engine developer millions of dollars.